What Should I Do?
Unexpected invitation
Stopped by the house today for some small things that fit in my backpack, no heavy moving today as it is raining. The main reason was to use the mini van for shopping, mainly stocking up on holiday cheer.
My son was in the toilet, of course, and called out from it as I came in, asking if I was coming over for Christmas. I did not answer. If asked, I will say I didn’t hear him. His mother was upstairs and did not hear either. I really do not want to be spending Christmas with those throwing me out. Not sure it is a concern as the preexwife has not indicated at all that she was expecting me, but if extended an invitation, I intend to politely turn it down.
He finally gave me some ideas for a Christmas Gift, two books. They are on order and will hopefully be in for pick up on Monday or Tuesday. Whenever they come in, I’ll wrap them and put them under their tree.
Mom sent cards two weeks age but they have not arrived. Hope they do tomorrow. She has been invited along with another recently widowed friend over to another widow’s home for finger foods and Halmark Holiday specials on Christmas. She and I will zoom Christmas morning, my time, which is Christmas Eve for her.

I have no advice other than to try and deal with your pending lonely holiday as positively as possible. Maybe read a thick book, eat well and exercise extensively. I have experience here. I strongly suggest that you avoid alcohol.
Based on what you have stated, making plans with your child and having him over should not be too difficult for you, and your wife might welcome the help. The tough part will be fighting over the method of treatment for your child's depression. By the way, your child has every right to be depressed. If I had the last five years as part of my childhood...I would be traumatized.